1. Field of the Invention
The invention is based on a piezoelectric actuator module, in particular for an injector in the high-pressure part of an injection system with the “common rail” injection system of a motor vehicle.
2. Description of the Prior Art
One actuator module of the type with which this invention is concerned is known in the industry and can be used in particular in conjunction with common rail injection systems for Diesel engines. The piezoelectric actuator module is assigned a valvelike valve control module and serves to actuate a valve closing body of the valve control module. By means of the valve control module, a nozzle needle of a nozzle module of the injection valve can be actuated in turn. The nozzle needle cooperates with at least one injection opening that leads to a combustion chamber of the engine.
The piezoelectric actuator module typically includes an actuator foot, which is braced on a housing of the injection valve; a piezoelectric element, which undergoes an expansion in length when an electrical voltage is applied; and an actuator head, by way of which the increase in length of the piezoelectric element is transmitted to a so-called adjusting piston in such a way that the adjusting piston is displaced axially. Via a hydraulic coupler embodied as a hydraulic chamber, the adjusting piston cooperates with a so-called actuating piston, which in turn is connected to the valve closing body. Such a construction is also described in German Patent Disclosure DE 199 46 831.
German Patent Disclosure DE 100 43 626 shows a piezoelectric actuator module that is surrounded by an axially extending sleeve, which serves to protect the piezoelectric element from dirt and fuel as well as from damage upon assembly. In the region of the actuator head, the piezoelectric actuator module is sealed off by means of a bellows, which on the one hand allows an actuator stroke and on the other is capable of compensating for a negative coefficient of temperature expansion on the part of the piezoelectric element.
However, bellows have the disadvantage that they require a relatively large amount of space and are expensive.